1. Field of the Invention
The invention is of catheters of enhanced biocompatibility, blood compatibility, and corrosion resistance, as well as superior low friction, flexibility, and corrosion characteristics. More specifically, the invention catheters are fabricated from relatively low modulus metals, such as zirconium or a zirconium-containing alloy, and are coated with blue to black zirconium oxide or zirconium nitride to provide enhanced blood compatibility, microfretting resistance, electrical insulation, and corrosion resistance where applicable.
2. Description of the Related Art
With advances in the technology for treating heart diseases, there has developed an increasing demand for sophisticated cardiovascular implants and surgical tools for use in cardiovascular surgery.
For example, vascular grafts are used to replace damaged blood vessels. These grafts may be fabricated from biocompatible organic polymers, such as woven dacron, silicone, polyurethane, and the like. Others are not of woven polymers, but are simply smooth cylindrical tube sections (i.e., allographs or autographs) that replace the section of removed artery or vein. While these grafts are fabricated from biocompatible polymers, it is frequently desirable to have a graft fabricated from a blood compatible metal that will retain its shape, not degrade with time, and not collapse under exerted pressure. While the buildup of a coating of certain blood components (such as endothelial cells) that provide a surface compatible with blood is desirable, the metal should desirably be resistant to a build up of adverse blood components on the graft surface which might ultimately impede the flow of blood through the graft.
It is currently known to use balloon-expandable stents to prop open blood vessels that have become damaged so that they are prone to collapse, or blood vessels that have become coated on the inside with plaque, thereby impeding the flow of blood. Typically, these stents are inserted by means of a guide wire with a stent in a collapsed state at its distal end. Once the stent is in position, a balloon positioned inside the stent is inflated so that the stent expands and props open the desired area of the blood vessel. Such stents are also used for gastrointestinal, urinary, and other non-cardiovascular applications.
Certain cardiac treatment procedures also require the use of pacemaker leads and other current-bearing leads that are usually coated with an insulative barrier that both electrically insulates and isolates the current-bearing core from body fluids. Currently, a typical pacemaker or other cardiovascular lead includes a central core of electrically conductive metal, usually cobalt-nickel alloy, coated with a polymeric insulative coating, usually polyurethane. However, polyurethane coatings eventually break down under the effect of body fluids and enzymes producing potentially harmful degradation products. Further, the polymer coating may crack or separate with time so that body fluids or adjacent wires come in contact with the electrical conductor and interfere with electrical signals. Further, the electrical conductor is then subject to corrosion due to body fluids.
In a typical defibrillator, a flexible silicone polymeric patch with a thinly coiled titanium, cobalt-nickel, or stainless steel wire is attached to the appropriate segment of heart muscle. A lead wire is attached to this coil for powering the coil to stimulate the heart muscle. The lead wire exits from the body to an external power source. The lead wire is frequently coated with polyurethane. Thus, this lead wire is both an electrical carrying device and a percutaneous device, in the sense that it penetrates the skin and exits from the body. However, it is coated with a relatively soft and fragile polymeric composition which provides limited protection to potential damage to lead sections carried outside the body. Thus, there is a need for a percutaneous lead that is crush resistant, biocompatible, and that provides suitable electrical conductance and insulation to isolate the electrical carrying lead from other lead wires and body tissue. Further, the lead should be resistant to chemical degradation in body fluids.
During surgery, guide wires may be inserted into blood vessels. These guide wires may be used to locate sensors, stents, leads, and other devices in specific areas, or may be equipped with cutting edges at their tips so that blood vessels may be surgically cleared of obstructions. In one of the commercially available guide wires, the wire includes a central core made of an elastic metallic alloy coated with a polyurethane jacket which is in turn coated with a hydrophilic material. This meets at least some of the requirements for a suitable guide wire, these requirements being that the exterior of the guide wire in contact with blood vessel tissue be of low friction with respect to the blood vessels, and that the guide wire be kink-resistant and flexible (low modulus) for maneuverability within the blood vessel. Also, the exterior surface of the guide wire in contact with the interior surface of a catheter (the catheter walls) should have low friction relative to the catheter wall material. Further, the guide wire should be radiopaque, to allow the surgeon to track the position of the guide wire within the blood vessel. Finally, the construction of the guide wire should be such as to allow adequate torque control, desirably so that one rotation at a control end of the guide wire leads to one rotation at the cutting edge tip of the guide wire. There yet exists a need for improved guide wires that can meet all these requirements and, additionally, have a high surface hardness to improve cutting edge sharpness and cutting edge durability.